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The influence of swirl on performance and emissions was investigated using a single cylinder Hydra research engine fitted with a high pressure electronic unit injector and a variable swirl mechanism. A large amount of emission data was collected together with the cylinder pressure, fuel line pressure and needle lift signals at a wide range of operating conditions. The influence of a fixed swirl ratio on emissions was also investigated on a Ford HSD425 York engine with conventional injection system and a synopsis of the results is discussed. Laser illuminated high speed cinematography was used to study the interaction of swirl with spray and combustion processes. Data is presented on air- fuel mixing, spray trajectories and flame movement at different operating conditions. Data is also presented to highlight the influence of swirl on the heat release rate, cylinder pressure rise and its relation to measured emission levels, particularly NOx and particulates.

A large number of high speed photographs have been taken of combustion in a high speed direct injection diesel engine. A frame rate of upto 20,000 frames/sec has been achieved at engine speeds up to 3000 rev/min. This has been achieved by computer controlled synchronization of a Cu-vapour laser illumination source, the high speed camera and the electronically controlled fuel injection equipment. In addition to the photography, the basic macroscopic parameters of combustion were recorded simultaneously: this enables the photographic information to be related to the heat release information. The parameters investigated include the influence of swirl ratio, injection system, engine speed, load, injection timing, and combustion chamber shape on spray and combustion. The influence of various parameters on spray growth, ignition and combustion is discussed. Combustion processes in open and reentrant open bowl combustion chambers are examined.

The atomisation characteristics of DI diesel engine fuel injection nozzles have been the subject of intensive study over the last decade. Much of this work has been related to clean, single hole nozzles spraying into quiescent air, at either ambient conditions or elevated pressures and temperatures. Experience shows that fuel injector nozzles may foul very rapidly in field service, and that this might have a significant effect on the performance of the engine particularly with regard to emissions. The build up of material on the injector nozzle can be controlled by the addition of suitable fuel additives. This paper describes test procedures developed to assess deposit build up and to indicate the efficacy of keep clean additives. The paper then goes on to describe high speed photographic techniques for studying the fuel spray characteristics of clean and fouled injectors in a firing engine.

An 8.5 inch bore two stroke engine has been modified into a photographic test rig in which pictures of the complete combustion chamber could be taken vertically upwards through a perspex crowned piston, using a high speed camera. Tests were carried out using several nozzles of the same total hole area. Two fuelling rates and three different air supply pressures were used. At each test condition thirteen cycles of fired data were recorded on 16 mm high speed colour film. At the same time synchronised transient cylinder pressure and fuel injection data were recorded using an on-line data acquisition system. Correlation of jet development from photographs with heat release deduced from the cylinder pressure diagrams using a standard single zone technique show differences due to changes in the hole configuration and in air supply pressure, with approximately constant fuel injection rates.

An extensive experimental program of in-cylinder sampling is described and the integrity of the res:u1ts discussed. The sampling data of the gaseous products NO, CO and CO2 have been used to produce concentration contours on various planes around the fuel spray at different times during the combustion process. Some calculations of spray penetration and NO production have been compared with experimental data.

The design and application of a high speed, timed, sampling valve for the extraction of gas samples, at a variety of points and times, from the combustion chamber of a medium speed diesel engine is described. The valve was traversed radially into the combustion chamber and combined with rotation of the central fuel injector gave sampling at sixteen points relative to the fuel spray. For any given sample the valve opened and closed at the same time each cycle. Samples were analysed and the levels of carbon monoxide, carbon dioxide and nitric oxide were recorded for the complete combustion process.

Heat release data have been obtained from a 5 in bore direct injection diesel engine operating over a range of conditions including off-design conditions, such as running at low air to fuel ratios, using six-hole injector nozzles in place of the standard three-hole nozzles, and reducing compression ratio and thereby swirl ratio at tdc. The paper shows that when operating with adequate utilized air fuel ratios (A/Fs) the experimental heat release data could be correlated with a single zone combustion model and that changing the number of nozzle holes or compression/swirl ratio had little effect on the correlation after the initial period of heat release. At inadequate A/Fs a modification to the model to allow for partial combustion was introduced. This improved correlation and enabled reasonable heat release prediction in the cycle synthesis program. Examples are given of heat release and cycle pressure diagrams computed using these models.